汽车座椅舒适性：乘客偏好与人体测量调节【中文7310字】
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汽车座椅舒适性:乘客偏好与人体测量调节【中文7310字】
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汽车座椅舒适性：乘客偏好与人体测量调节Mike Kolich*加拿大安大略省温莎市温莎大学工业与制造系统工程系，N9B-3P42002年2月20日收到; 2002年9月28日接受摘要：如果不考虑目标人群的舒适期望，就无法建立汽车座椅设计规范。已发表的文献支持这一论点，该文献表明人体工程学标准，特别是与生理学相关的标准，不能满足消费者的舒适度。本文的目的是以同样的方式挑战与人体测量学相关的人体工程学标准。在这种情况下，代表各种体型的12名受试者在短期座位会议期间评估了五种不同的紧凑型汽车座椅。为此目的使用了一系列可靠有效的调查。五种轮廓和几何特征座位被量化并与调查信息进行比较。在公布的人体测量调节标准和受试者优选的腰部高度，座椅靠背宽度，垫子长度和垫子宽度之间发现了差异。基于这一发现，得出的结论是汽车座椅的舒适性是一门独特的科学。人体工程学标准虽然是这门科学的基础，但不能盲目应用，因为它们无法确保舒适的汽车座椅。 关键词：汽车座椅;舒适;人体测量学1.简介从许多不同的角度研究了座椅舒适性的人体工程学（Zhang et al。1996; Yamazaki，1992）。作为概括，目前的做法是设计汽车座椅以满足人体工程学标准（人体工程学指南的同义词）。假设这种方法转化为积极的消费者舒适度评级。出于本文的目的，有两类人体工程学标准。它们是生理学和人体测量学。传统上使用肌电图（Bush et al。1995; Lee and Ferraiuolo，1993; Sheridan et al。1991），椎间盘压力测量（Andersson）来量化处理肌肉，椎间盘，关节和皮肤的生理因素。 et al，1974），振动传递率（Ebe和Griffin，2000），乘员座位界面的压力分布（Kamijo等，1982; Hertzberg，1972），以及乘员座位界面的微气候（Diebschlag）等人，1988）。然而，与生理学相关的人体工程学标准受到严格审查，特别是在过去十年中。（里德等人. 1991），例如，描述了汽车座椅设计师的困境，因为需要在规定生理上合适的坐姿和适应驾驶员的首选姿势之间取得平衡。他们认为，规定的姿势有时会影响长期的安慰。后来，里德等人。 （1995年），基于他们的初步数据，强调了传统的设计汽车座椅靠背以诱导大量腰椎前凸的实践之间的不相容性（根据Andersson等人，1974，从生理角度来看，这是合适的）和理想的满足乘员选择的脊柱结构（对于一些住院患者来说，更具脊柱活性）.Reed和Schneider（1996）在后续研究中证实了这种不相容性.Kolich等（2000），在他们的调查中得出了类似的结论。这些研究都表明人体具有很大的可塑性以适应各种各样的坐姿。因此，基于生理学的人体工程学标准，因为它们不能确保舒适性，可能会不必要地限制汽车座位设计。在很大程度上由于Akerblom（1948）的工作，与人体测量学相关的人体工程学标准一直被认为是舒适座椅的一个关键方面。从这个角度来看，设计师必须确保座椅中的一系列人，从小到大。一般而言，汽车座椅设计是通过针对目标人群注意到适当的人体测量维度（通常为第5百分位女性和第95百分位男性）的约束值来指定的。通过可调节性最好地实现腰部舒适的住宿。在大多数应用的情况下，由于相关的成本，这通常是不切实际的。据Reed等人说。 （1994年），腰部轮廓的顶点应位于距离H点105至150毫米之间。另外，在汽车座椅行业中，H-Point引用了许多人体测量尺寸，这是基于人体模型的臀部点，代表中型男性如何坐在不同的车辆座椅和车辆环境中并与之互动（汽车工程师协会，1995年）。上述范围被认为是在坐姿中捕捉小女性和大男性的L3关节水平。在上部座椅靠背（大约在胸部高度处），最小宽度应该支撑斜倚时大型男性的胸部宽度。在后腋窝褶皱之间的背部测量的间隙距离是适当的人体测量参考测量值。据Reed等人说。 （1994），471毫米应该容纳95的男性间隙距离。不满足此标准可能会损害座椅靠背侧向支撑。缓冲长度是大腿支撑的重要决定因素。太长的垫子可以在膝盖附近的乘客腿部的后部施加压力。这个区域的压力会导致局部不适，并限制血液流向腿部（Reed等，1994）。缓冲长度受到第5百分位女性群体的臀部到pop窝长度的限制。这个尺寸是在坐着的乘员从臀部的最后面的投影到膝盖后面的pop窝折叠处测量的。戈登等人。 （1989）报道了第5百分位女性臀部到pop窝的长度为440毫米。这相当于距离H点大约305 mm。该维度/标准是最大值。在坐垫宽度的情况下，第95百分位女性坐位宽度被用作特定限制，因为该度量超过第95百分位男性坐位宽度。使用人体调节原则，最小缓冲宽度必须大于第85百分位女性坐位宽度432毫米（Gordon等，1989）。然而，需要更大的最小缓冲宽度，主要是因为所引用的人体测量值不包括衣服的余量（汽车座椅通常必须适合在穿着厚衣服的寒冷气候中使用）。里德等人。 （1994）认为汽车座椅应在臀部提供500毫米的间隙。该特性影响垫侧向支撑。必须先对舒适度的主观感知进行量化，然后才能将其与人体测量学相关的人体工程学标准进行比较。在汽车座椅行业，结构化调查通常用于此目的。缺乏对座椅舒适度调查设计的重视（例外包括Reed等，1991; Shen和Parsons，1997; Kolich，1999）令人惊讶，因为（1）座椅舒适性发展依赖于调查数据的程度和（2）事实上，许多与主观数据收集有关的问题已经有一段时间了。一项好的调查是可靠和有效的。这涉及将调查措施分为两个部分：真实分数部分和测量误差部分。可靠的调查项目包含很少的测量误差。但是，不可能直接观察调查项目上实际分数的真实分数和误差分量。相反，相关技术用于估计调查项目反映真实分数而不是测量误差的程度。有效性是指从调查中获得的数量/分数是否真正反映了研究人员打算测量的内容。有效性与可靠性有关，尽管不同。可靠的措施提供一致的读数，但不一定有效。另一方面，除非测量也可靠，否则测量不可能有效。一般而言，可靠性是有效性的必要条件，但不是充分条件，可靠性将上限设置为可以预期在度量中找到的有效性水平。可靠性和有效性的重要指标是重测信度，内部一致性，标准相关有效性，构造相关有效性和面部有效性（Kolich，1999）。通过考虑以下原则可以确保可靠性和有效性：（a）调查项目的措辞（Oppenheim，1966），（b）评级量表类别的数量（Guilford，1954; Grigg，1978），（c）口头表达与类别相关的标签（Osgood等，1957），以及（d）受访者的兴趣和动机，作为调查长度的函数。还必须考虑评定量表的类型（即名义，序数，间隔或比率），因为座椅舒适度调查通常需要进行某种形式的定量分析，无论是简单的频率计数还是更复杂的统计处理（Stevens，1946; Cozby，1989）。采用的统计分析类型取决于收集数据的方式。如果不参与调查设计的定量方面，将产生最多有偏见的结果，最坏的情况是完全无效。实际上，Kolich（1999）认为缺乏高质量的主观数据阻碍了汽车座椅舒适性发展的进步。虽然研究人员可能倾向于设计包含许多项目的调查，但如果不考虑可靠性和有效性，那么可以在结果中存在有限的信心。 Kolich（1999）的立场是，就调查项目而言，更多并不总是更好。2.目的本文基于使用Kolich（1999）调查的部分收集的主观数据以及汽车座椅行业已经实现的可能是与生理学相关的人体工程学标准的怀疑，旨在挑战与人体测量学相关的公布的人体工程学标准。我们的想法是，使用人体测量学考虑而开发的设计规格无助于舒适座椅的生产。也就是说，消费者对汽车座椅舒适性的期望并不一定通过人体测量调节来满足。3.方法为了获得设计数据，从租赁公司获得了五十九年车型，并且驾驶员座椅轮廓被扫描，而在实际车辆中，使用便携式坐标测量机（CMM），称为FaroArm（如图1所示） 。根据制造商的说法，FaroArm的球形直径为3.7米，重7千克，精确到0.18毫米。图1。 FaroArm用于扫描汽车座椅。相隔约1个月评估的席位为基准水平即带手动轨道（2向）和躺椅的布料。每辆由不同制造商生产的车辆均选自北美紧凑型轿车细分市场。假设来自相同细分市场的座椅具有相当的座椅高度，这是乘员套件的主要决定因素。部分由于座椅高度的差异，部分原因是特征内容的差异，来自不同细分市场的座位难以比较。考虑到所有因素，座位被认为准确地反映了市场细分的范围。读者将注意到，在本文中，座位使用字母A到E来区分。座位未被命名，因为车辆制造商没有寻求许可，因此不允许这样做。为了公平地比较轮廓和几何特征，五个座位的设置类似。在汽车座椅行业，由于座椅设计各不相同，制造商指定的设计位置是比较座椅的标准方式。出于本研究的目的，无法获得此信息。因此，建立了一个协议来估计每个座位的设计位置。它如下：1. 座椅靠背角度从垂直方向设定为251。 2.赛道位置设置为全后方。3. H-Point人体模型（汽车工程师协会，1995）被放置在座位上（没有重量）。4.调整座椅，直到H-point人体模型充分定位在踏板和方向盘前方。5.根据汽车工程师协会（Society of Automotive Engineers，1995）开发的标准装载H-Point人体模型（即加入重量）。6.在这个位置，确定每个座位的H点到脚跟点关系和H点人体模型的临界角（即躯干，臀部，膝盖和脚）。 表1概述了此信息，默认情况下，定义了可被视为紧凑型汽车细分市场代表的限制。将座椅设置到估计的设计位置（如表1所示）后，使用FaroArm创建了一个对齐。该对齐用于建立坐标系（x; y;和z平面）。相对于车辆的坐标系可以在图2中可视化.XZ平面用于限定座椅的中心线（即，座椅的内侧和外侧边缘之间）。两个独立的YZ平面，一个用于座椅靠背，一个用于座垫，定义了横车部分。对于每个座椅，座椅靠背平面旋转到估计的设计位置躯干角度（参见表1）。缓冲平面没有旋转。点之间的最小距离设定为0.1毫米。这基本上用于通过点过滤并删除冗余数据。作为实际扫描过程的一部分，探头在选定的平面上来回传递。每次探头通过飞机时，一个点被数字化。一旦足够，收集数据点，AnthroCAMTM（Faro Technologies，Inc.，1998）用于在每个指定平面中“连接点”。表格1紧凑型汽车限制H点机器角度和H点到脚跟点关系座椅A 座椅B 座椅C 座椅D 座椅E 平均 STD躯干角（度） 24 24 24 23.5 24 23.9 0.2髋角（度） 96.1 98 96 95 97.3 96.5 1.2膝角（度） 129.8 131 127.5 127 128 128.7 1.7脚角（度） 87.9 85 87 89.5 87.5 87.4 1.6H点到脚跟点-x（mm）887 833 868 837 857 856.4 22.3H点到脚跟点-z（mm）223 246 222 169 243 220.6 30.9图2。 用于扫描过程的坐标系（采用汽车工程师协会，1998年）。点被带到探针的中心。因此，在后处理操作中，扫描线被探针的半径（即3mm）偏移。每条扫描线都单独偏移。这是一个AutoCAD功能（Autodesk，Inc，1996）。除轮廓外，H点（在估计的设计位置）被数字化。为了执行这项任务，H-Point人体模型再次被放置在座位上。作为分析的一部分，H-Point与一些座椅轮廓和几何特征有关。完成扫描，其中一个例子包含在图3中，然后确定尺寸以确定设计参数。在这项研究中，在轮廓扫描的两个最宽点之间测量H点处的垫宽（对应于臀部宽度）和高于H点的座椅靠背宽度（对应于胸部高度）300 mm（图4 - 代表一个典型的跨车部分）。缓冲长度测量为从H点到衬垫前缘的水平距离。腰部轮廓的顶点的位置被测量为座椅靠背轮廓切线上的最突出点并且平行于设计位置躯干线。识别后，通过垂直于躯干线的顶点绘制一条线。从该线沿躯干线到H点测量顶点的高度。缓冲长度和腰部高度在图5中可操作地定义，其代表典型的中心线部分。如图3. 完成座椅扫描的示例（等轴测视图）。图4. 从扫描数据（YZ平面）的车辆截面获得的尺寸的操作定义。图5.从扫描数据（XZ平面）的中心线部分获得的尺寸的操作定义。在扫描每个座位后，12名受试者完成了表2中所示的调查。该调查旨在评估陈列室的舒适度。虽然人们承认短期评估并未涵盖汽车座椅舒适性的所有方面泡沫的物理特性，例如，随着时间的推移而变化，这可能对长期舒适度（即乘坐质量）更重要，该调查适用于本研究的目的。换句话说，人们认为，作为实验方案的一部分收集的短期主观数据，因为它们专注于座椅轮廓/几何形状的特定方面，可用于比较乘员偏好和与人体测量调节相关的标准。值得说明的是，没有提供“正确”或“不舒服”构成的参考值（即与本研究中的评定量表相关的口头质量）。这是因为参考价值不是为消费者定义的，因为消费者有机会对市场中的车辆/座位进行评级。通过这种方式，该研究被认为反映了“真实世界”的舒适度。在完成四个调查项目之前，允许受试者将座位调整到舒适的位置。同样的12名受试者评估了每个五个座位。调查项目的数量不被视为限制。包含具有可靠性和有效性水平的项目比包含大量项目更重要。通过从先前发布的调查中选择项目来确保可靠性和有效性 - 该调查证明了可靠性和有效性水平（Kolich，1999）。此外，调查项目是特别选择的，因为他们与感兴趣的设计方面的假设关系（例如腰部舒适度与腰部轮廓顶点的高度，后侧向舒适度与椅背宽度+ 300毫米，从H点，大腿H-Point的舒适性与缓冲垫长度，缓冲侧向舒适度与缓冲垫宽度的关系。表2座椅舒适度调查（改编自Kolich，1999）类目 1 2 3 恰到好处缺点木材的舒适度 不舒服背侧舒适 不舒服垫子大腿 不舒服坐垫侧面舒适度 不舒服表3五个汽车座椅的测量尺寸（mm）座椅A 座椅B 座椅C 座椅D 座椅E 平均 STDH-Point的腰椎尖端高度89 124 116 143 143 123.0 22.4胸背处的背部宽度 451 508 514 507 462 488.4 29.5H-Point缓冲长度 351 341 362 352 357 352.6 7.8臀部缓冲宽度 428 484 481 445 414 450.4 31.34.结果和讨表3显示了从扫描数据获得的座椅尺寸。还提供了描述性统计。关于来自H-Point的腰椎顶点的高度，只有座位A不满足Reed等人（1994）的人体测量调节标准105-150mm。座椅B-D超过座椅靠背宽度，胸部水平要求为471毫米（Reed等，1994）。值得注意的是，所有五个座位都不能满足305和500毫米的座垫长度和坐垫宽度的人体测量标准（Reed等，1994）。表4列出了以自我报告方式获得的样本的人体测量和人口统计细节。三维人体测量数据通过激光扫描获得，如美国民用和欧洲表面人体测量资源（CAE-SAR）项目（Robinette等，1999）本来是理想的。不幸的是，获得这种类型的数据是昂贵的，耗时的，并且依赖于设备的命题。本研究无法获得所需的资源。注意，表4中列出的百分位数值来自Gordon等人。（1989年）。表4表明表示了大范围的体型（即第3至第99百分位的男性站立高度和第5至第99男性体重）。然而，这项研究不能用于确定座椅设计的特定方面如何影响不同的人体测量组（例如短，中，高），因为操作人体测量测量（例如坐姿中L3关节水平的高度，不考虑间隙距离，臀部到pop窝长度和坐臀宽度。未来的研究应该努力包括更完整的主题样本的人体测量特征。表4评估五个座位的受试者的人体测量和人口统计学特征主题 性别 站立身高（cm） 百分位 体重（kg） 百分位数1 女 90 176 55 202 男 98 189 132 993 男 99 198 105 984 女 179 99 73 905 男 98 189 82 656 女 99 178 73 907 女 15 35 61 508 男 45 175 79 559 女 101 54 64 6010 男 172 30 85 7511 女 15 2 5 73 9012 男 164 3 61 5STD 154 42 130表5中列出了四个调查项目的描述性统计数据。粗略地检查这些信息表明座位不是同样舒适，而座位C相对于所有四个项目而言，表现最佳（最接近对）。实际上，座椅C也具有最小的标准偏差，暗示乘客倾向于同意他们对舒适性的看法。表5从调查中得出的主观评级的描述性统计数据座椅A 座椅B 座椅C 座椅D 座椅E 整体调查项目平均STD平均STD平均STD平均STD平均STD平均STD腰部舒适度0.6 0.7 1.3 0.5 0.2 0.4 0.7 0.5 1.4 0.7 0.8 0.5背侧舒适度0.7 0.5 1.1 0.7 0.3 0.5 0.8 0.6 1.4 0.5 0.9 0.4大腿舒适度0.8 0.7 1.4 0.8 0.2 0.4 1.3 0.9 1.4 0.5 1.0 0.5缓冲侧向舒适度0.7 0.5 0.8 0.5 0.1 0.5 0.7 0.5 1.3 0.7 0.7 0.4测试表5中的差异以获得统计学意义。这里采用的方法是检验表5中列出的平均值相等的假设。在汽车行业中，调查数据的统计处理是争议的根源。大多数座位舒适度调查都使用序数量表 - 就像本次贡献中使用的调查一样。无论知情与否，座位系统设计团队由于其统计处理调查数据的复杂方式，基本上至少假设一个区间尺度（如果不是比率）。根据Stevens（1946）领导的一个学派所说，这是不正确的。史蒂文斯（1946）认为，不应使用参数统计分析序数据。竞争学派拒绝这一前提，声称尽管可能引入了错误，但它被更强大和更好的统计数据的使用所抵消（Labovitz，1972）。感兴趣的读者可以参考Kolich（1999），以获得关于将参数统计应用于有序数据的可接受性的更详细讨论。本文赞同第二种思想流派。基于该位置，使用单向ANOVA，其是假设数据正态性的参数统计检验（表6证明数据在0.05水平是正常的），用于测试先前陈述的假设。表7中显示的ANOVA结果显示，座位之间存在统计学上的显着差异（判断标准为0.05）。 所有四个调查项目都是如此。表6 Kolmogorov-Smirnov Z检验调查数据的正态性调查项目 K-S Z测试 p值腰部舒适度 2.003 0.001背部侧舒适度 2.246 0.000大腿舒适度 1.803 0.003坐垫侧向舒适度 2.418 0.000表7座位间调查差异的单因素方差分析平方和 df 均方 F Sig座椅之间的腰部舒适度 13.500 4 3.375 11.027 0.000座位内 16.833 55 0.306总计 30.333 59座椅之间的侧向舒适性 9.233 4 2.308 7.734 0.000座位 16.417 55 0.298总计 25.650 59座椅之间的大腿舒适度 14.100 4 3.525 7.505 0.000座位数 25.833 55 0.470总计 39.933 59坐垫侧面舒适性座位之间 9.433 4 2.358 8.552 0.000座位 15.167 55 0.276总计 24.600 59表8与人体测量标准相比的乘员偏好舒适性至关重要 设计特性 人体测量标准（mm） 乘员偏好（mm）腰部支撑 H点的腰椎高度 105-150 90-123椅背侧向 支撑胸部高度 471 X514大腿 支撑垫长 o305 X362坐垫侧向支撑 臀部宽度 500 446-483在一致考虑时，前面的信息表明，与人体测量学相关的人体工程学标准与对舒适性的主观感知之间存在差异。例如，考虑这样一个事实，即满足与人体测量学相同的人体工程学标准的座椅可以获得显着不同的舒适度。例如，座椅B-E满足腰部高度要求，但主观评级表明座椅不能提供相当水平的腰部舒适度。代替这一点，可能更适合修改设计规范以适应表现最佳的座位，就所有四个调查项目而言，座位C.这在表8中完成。目前的贡献假设舒适方面是独立的。然而，例如，腰部舒适性可能受到大腿舒适性的影响是合理的。作为未来研究的一部分，应调查各种座椅舒适性方面的相互依赖性。这项研究表明，使用与人体测量学相关的人体工程学标准设计的汽车座椅不一定被认为更舒适。事实上，这些差异对于影响设计实践非常重要，特别是在包装和座椅轮廓/几何形状开发方面。例如，在垫子宽度的情况下，基于乘员偏好，公布的人体测量标准过于慷慨。这是一个值得关注的问题，因为在当今的环境中，室内空间非常宝贵。由于这种不匹配，汽车座椅可能消耗车辆内部的宝贵空间;否则，可用于其他功能的空间。同时，与人体测量相关的人体工程学标准在缓冲长度和座椅靠背宽度方面可能不足。也就是说，乘员似乎更喜欢更长的靠垫和更宽的椅背。腰椎区域的设计范围，一个记录良好的问题区域，可以正确地降低和缩小。这可能有助于减少腰椎疾病的频率和/或严重程度。5.结论本文发现已公布的人体测量调节标准与乘员偏好之间存在差异，这些偏好与腰部轮廓的顶点高度，座椅靠背宽度，坐垫长度和坐垫宽度有关。 基于这一发现，得出的结论是，虽然设计师理解相关的人体工程学（尤其是生理学和人体测量学）非常重要，但汽车座椅的舒适性是一门独特的科学。 因此，应该对此进行研究。 这涉及到目标人群的优先考虑因素。 只有这样，开发过程才能确保舒适的汽车座椅。Applied Ergonomics 34 (2003) 177184 Automobile seat comfort: occupant preferences vs. anthropometric accommodation Mike Kolich* Department of Industrial accepted 28 September 2002 Abstract Automobile seat design specifi cations cannot be established without considering the comfort expectations of the target population. This contention is supported by published literature, which suggests that ergonomics criteria, particularly those related to physiology, do not satisfy consumer comfort. The objective of this paper is to challenge ergonomics criteria related to anthropometry in the same way. In this context, 12 subjects, representing a broad range of body sizes, evaluated fi ve different compact car seats during a short-term seating session. Portions of a reliable and valid survey were used for this purpose. The contour and geometry characteristics of the fi ve seats were quantifi ed and compared to the survey information. Discrepancies were discovered between published anthropometric accommodation criteria and subject-preferred lumbar height, seatback width, cushion length, and cushion width. Based on this fi nding, it was concluded that automobile seat comfort is a unique science. Ergonomics criteria, while serving as the basis for this science, cannot be applied blindly for they do not ensure comfortable automobile seats. r 2003 Elsevier Science Ltd. All rights reserved. Keywords: Automobile seat; Comfort; Anthropometry 1. Introduction The ergonomics of seat comfort has been studied from a number of different perspectives (Zhang et al., 1996; Yamazaki, 1992). As a generalization, the current practiceistodesignautomobileseatstosatisfy ergonomicscriteria(synonymouswithergonomics guidelines). This approach is assumed to translate into positive consumer comfort ratings. For the purposes of this paper, there are two categories of ergonomics criteria. They are physiological and anthropometric. The physiological factors, which deal with muscles, vertebral discs, joints, and skin, have traditionally been quantifi ed using electromyography (Bush et al., 1995; Lee and Ferraiuolo, 1993; Sheridan et al., 1991), disc pressure measurement (Andersson et al., 1974), vibra- tion transmissibility (Ebe and Griffi n, 2000), pressure distribution at the occupantseat interface (Kamijo et al., 1982; Hertzberg, 1972), and microclimate at the occupantseatinterface(Diebschlagetal.,1988). Ergonomics criteria related to physiology have, how- ever, come under scrutiny, particularly in the past decade. Reed et al. (1991), for example, described the automobile seat designers dilemma as the need for a balance between prescribing a physiologically appro- priate seated posture and accommodating a driver in a preferred posture. They reasoned that prescribed pos- tures sometimes compromise long-term comfort. Later, Reed et al. (1995), based on their preliminary data, highlighted the incompatibility between the traditional practice of designing automobile seatbacks to induce a large degree of lumbar lordosis (which is, according to Andersson et al., 1974, appropriate from a physiological perspective and the ideal of satisfying occupant-selected spinal confi gurations (which, for some occupants, are more kyphotic). Reed and Schneider (1996) verifi ed this incompatibility in a follow-up study. Kolich et al. (2000), in the context of their investigation, came to a similar conclusion. These investigations all suggest that the human body has a great plasticity to adapt to a large variety of sitting conditions. For this reason, ergonomics *Corresponding author. Automotive Systems Group, Johnson Controls Inc., 49200 Halyard Drive, Plymouth, MI 48170, USA.Tel.: +1-734-254-5911; fax: +1-734-254-6277. E-mail address: michael.kolich (M. Kolich). 0003-6870/03/$-see front matter r 2003 Elsevier Science Ltd. All rights reserved. PII: S 0003 -6870(02 )0 0142-4 criteria based on physiology, because they do not ensure comfort, may unnecessarily limit automobile seat de- sign. Due in large part to Akerbloms (1948) work, ergonomics criteria related to anthropometry have long been considered a key aspect of comfortable seating. From this perspective, designers must ensure that a range of people, from small to large, fi t in the seat. In general, automobile seat designs are specifi ed by noting, for a target population, the constraining values of appropriate anthropometric dimensions (usually 5th percentile female and 95th percentile male). Comfortable accommodation in the lumbar region is best achieved through adjustability. This is, in the context of most applications, often impractical, due to the associated cost. According to Reed et al. (1994), the apex of the lumbar contour should be positioned between 105 and150mm from H-Point. As an aside, in the automotive seating industry, many anthropometric dimensions are referenced from H-Point, which is based on the hip point of a manikin that represents how medium-sized men sit in, and interact with, different vehicle seats and vehicle environments (Society of Automotive Engineers, 1995). This aforementioned range is thought to capture the L3 joint level for both small females and large males in the sitting posture. In the upper seatback (at approximately chest height), the minimum width should support the chest breadth of a large male when reclining. The interscye distance, measured across the back between the posterior axillary folds,isanappropriateanthropometricreference measurement. According to Reed et al. (1994), 471mm should accommodate the 95th percentile male interscye distance. Failure to satisfy this criterion may compro- mise seatback lateral support. Cushion length is an important determinant of thigh support. A cushion that is too long can put pressure on the posterior portion of the occupants legs near the knee. Pressure in this area will lead to local discomfort and restricted blood fl ow to the legs (Reed et al., 1994). Cushionlengthisconstrainedbythebuttock-to- popliteal length of the 5th percentile female segment of the population. This dimension is measured on the seated occupant from the rearmost projection of the buttocks to the popliteal fold at the back of the knee. Gordon et al. (1989) reported a 5th percentile female buttock-to-popliteal length of 440mm. This equates to approximately 305mm from H-Point. This dimension/ criterion is a maximum. In the case of cushion width, the 95th percentile female sitting hip breadth is used as a specifi cation limit, since this measure exceeds the 95th percentile male sitting hip breadth. Using the principle of anthropo- metric accommodation, the minimum cushion width must be greater than the 95th percentile female sitting hip breadth of 432mm (Gordon et al., 1989). However, a larger minimum cushion width is required, mainly because the cited anthropometric measurement does not include a margin for clothing (an automobile seat must generally be suitable for use in cold climates where heavy clothing is worn). Reed et al. (1994) believe that automobile seats should provide a clearance of 500mm at the hips. This characteristic affects cushion lateral support. Subjective perceptions of comfort must be quantifi ed before they can be compared to ergonomics criteria related to anthropometry. In the automotive seating industry, structured surveys are commonly used for this purpose. The lack of emphasis on seat comfort survey design (exceptions include Reed et al., 1991; Shen and Parsons, 1997; Kolich, 1999) is surprising given (1) the extent to which seat comfort development relies on survey data and (2) the fact that many of the problems related to the collection of subjective data have been well known for some time. A good survey is reliable and valid. This involves reducing the survey measures into two components: a true score component and a measurement error compo- nent. A reliable survey item contains little measurement error. It is, however, impossible to directly observe the true score and error components of an actual score on a survey item. Instead, correlation techniques are used to give an estimate of the extent to which the survey item refl ects true score rather than measurement error. Validity refers to whether the number/score obtained from the survey truly refl ects what the researcher intended to measure. Validity is related to, although different than, reliability. A reliable measure provides consistent readings but is not necessarily valid. On the other hand, a measurement is unlikely to be valid unless it is also reliable. In general, reliability is a necessary but not suffi cient condition for validity, with reliability setting the upper bound to the level of validity that one can expect to fi nd in a measure. Important indicators of reliability and validity are testretest reliability, internal consistency, criterion-related validity, construct-related validity, and face validity (Kolich, 1999). Reliability and validity can be assured by considering the following principles: (a) the wording of survey items (Oppenheim, 1966), (b) the number of rating scale categories (Guilford, 1954; Grigg, 1978), (c) the verbal tags associated with the categories (Osgood et al., 1957), and (d) the interest and motivation of the respondent, as a function of survey length. The type of rating scale (i.e. nominal, ordinal, interval, or ratio) must also be considered, since seat comfort surveys are, typically, subjected to some form of quantitative analysis, whether it is a simple frequency count or a more complex statistical treatment (Stevens, 1946; Cozby, 1989). The type of statistical analysis employed is dependent on the manner in which the data were collected. Failure to attend to the quantitative aspects of survey design will M. Kolich / Applied Ergonomics 34 (2003) 177184178 produce results that are, at best, biased and, at worst, totally invalid. In fact, Kolich (1999) believes that the lack of quality subjective data has hindered advances in automobile seat comfort development. While research- ers may be tempted to devise surveys with many items, if reliability and validity are not considered, then there is limited confi dence that can be placed in the results. Kolichs (1999) position is that, in the case of surveys items, more is not always better. 2. Objective This paper, on the basis of subjective data collected using portions of Kolichs (1999) survey and spurred by what the automotive seating industry has realized may be questionable ergonomics criteria related to physiol- ogy, intends to challenge the published ergonomics criteria related to anthropometry. The thought is that design specifi cations developed using anthropometric considerations do not contribute to the production of comfortable seats. That is, consumer expectations of automobile seat comfort are not necessarily satisfi ed through anthropometric accommodation. 3. Method To obtain design data, fi ve 1997 model year vehicles were obtained from rental agencies and the driver seat contours were scanned, while in the actual vehicles, using a portable coordinate measurement machine (CMM), known as a FaroArm (displayed in Fig. 1). The FaroArm had a 3.7m spherical diameter, weighed 7kg, and was, according to the manufacturer, accurate to within 0.18mm. The seats, which were evaluated approximately 1 month apart, were base level i.e. cloth with manual track (2-way) and recliner. The vehicles, each produced by a different manufacturer, were selected from the North American compact car segment. Seats from the same market segment are assumed to have comparable seat heights, which is a primary determinant of occupant package. Owing partly to the difference in seat height and partly to the difference in feature content, seats from different market segments are diffi cult to compare. Allthingsconsidered,theseatswerethought to accurately refl ecttherangefoundinthemarket segment. The reader will note that, in this paper, the seats are distinguished using the letters A through E. The seats were not named because permission was not sought from and therefore granted by the vehicle manufacturers. To fairly compare the contour and geometry char- acteristics, the fi ve seats were similarly set-up. In the automotive seating industry, because seat designs vary, manufacturer-specifi ed design position is the standard way to compare seats. This information could not be obtained for the purposes of this research. As a consequence, a protocol was established to estimate each seats design position. It was as follows: 1. The seatback angle was set to 251 from vertical. 2. The track position was set to full rear. 3. The H-Point manikin (Society of Automotive En- gineers, 1995) was placed in the seat (without weights). 4. The seat was adjusted until the H-Point manikin was adequately positioned in front of the pedals and steering wheel. 5. The H-Point manikin was loaded (i.e. weights were added) according to the standard developed by the Society of Automotive Engineers (1995). 6. In this position, the H-Point to heel point relation- ships and the H-Point manikins critical angles (i.e. torso, hip, knee, and foot) were determined for each seat. Table 1 outlines this information and, by default, defi nes limits that can be considered repre- sentative of the compact car segment. After setting the seat to the estimated design position (shown in Table 1), an alignment was created with the FaroArm. This alignment was used to establish a coordinate system (x; y; and z plane). The coordinate system, in relation to the vehicle, can be visualized in Fig. 2. An XZ plane was used to defi ne the centerline of the seat (i.e. between the inboard and outboard edges of the seat). Two separate YZ planes, one for the seatback and one for the cushion, defi ned the cross car sections.Fig. 1. FaroArm used to scan automobile seats. M. Kolich / Applied Ergonomics 34 (2003) 177184179 For each seat, the seatback plane was rotated to the estimated design position torso angle (refer to Table 1). The cushion plane was not rotated. The minimum distance between points was set to 0.1mm. This, basically, served to fi lter through points and delete redundant data. As part of the actual scanning process, the probe was passed back and forth over the selected plane. Each time the probe passed over the plane a point was digitized. Once enough, data points were collected, AnthroCAMTM(Faro Technologies, Inc., 1998) was used to connect the dots in each of the specifi ed planes. Points were taken to the center of the probe. For this reason, the scan lines, in a post processing operation, were offset by the radius of the probe (i.e. 3mm). Each scan line was offset individually. This was an AutoCAD function (Autodesk, Inc, 1996). In addition to the contour, the H-Point (in estimated design position) was digitized. To perform this task, the H-Point manikin was, once again, placed in the seat. The H-Point was, as part of the analysis, related to some of the seat contour and geometry characteristics. The fi nished scan, an example of which is included in Fig. 3, was then dimensioned to defi ne design para- meters. For this study, cushion width at H-Point (corresponding to hip breadth) and seatback width 300mm superior to H-Point (corresponding to chest height) were measured between the two widest points on the contour scan (Fig. 4which represents a typical cross car section). Cushion length was measured as the Table 1 Compact car limits for H-Point machine angles and H-Point to heel point relationships Seat ASeat BSeat CSeat DSeat EMeanSTD Torso angle (deg)24242423.52423.90.2 Hip angle (deg)96.198969597.396.51.2 Knee angle (deg)129.8131127.5127128128.71.7 Foot angle (deg)87.9858789.587.587.41.6 H-Point to heel pointx (mm)887833868837857856.422.3 H-Point to heel pointz (mm)223246222169243220.630.9 Fig. 2. Coordinate system used for the scanning process (adopted from Society of Automotive Engineers, 1998). Fig. 3. Example of fi nished seat scan (isometric view). M. Kolich / Applied Ergonomics 34 (2003) 177184180 horizontal distance from H-Point to the leading edge of the cushion. The location of the apex of the lumbar contour was measured as the most prominent point on the seatback contour tangent and parallel to the design position torso line. Once identifi ed, a line was drawn through the apex that was perpendicular to the torso line. The height of the apex was measured from this line along the torso line to the H-Point. Cushion length and lumbar height are operationally defi ned in Fig. 5, which represents a typical centerline section. After each seat was scanned, 12 subjects completed the survey shown in Table 2. The survey was designed to assess showroom comfort. While it is acknowledged that short-term evaluations do not capture all aspects of automobile seat comfort the physical properties of foam, for example, change over time, which is probably more important to long-term comfort (i.e. ride quality), the survey was appropriate in the context of this studys purpose. In other words, it
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